xMax meets Shannon

xMax is a technology developed by xG Technology. According to their web page “xG Flash Signal uses breakthrough single cycle modulation to deliver longer range and lower power RF communications. Single cycle modulation is implemented when individual sinusoidal cycles of RF energy are modulated to represent one or more bits of data.” In an article published in Computer we find the following statement: “Thus, Bobier said, xMax can use 1,000 to 100,000 times less power than comparable transmission technologies. This greatly benefits wireless systems, which operate on limited battery resources.” A search of the web reveals a fairly large number of articles making similar claims.

Given the state of the art of wireless communication this claim is quite incredible. In a fair comparison (same data rates, same bit-error-rate, same bandwidth, same antennas, same pathloss, same interference/noise conditions) it would be remarkable if any communication system could reduce the required transmit power even by, say, a factor of 5 compared to existing communication systems such as WiMax or one of the cellular systems. The reason for that is that modern communication systems are highly advanced and already operate very close to the performance limits dictated by the Shannon theorem. Claiming that a new modulation technique can operate with orders of magnitude less power (in a fair comparison!) is so far beyond the realm of possibility as to not deserve further discussion.

We should emphasize that there is no reason to believe that the xMax technology does not work. There are many ways, including new and innovative ways, to design wireless communication systems. However, such systems can not operate with significantly lower transmit power than comparable existing technologies. Thus, there is every reason to believe that xMax, in a fair comparison, will require an amount of transmit power comparable to that of existing transmission technologies. This is true regardless of how new or different xMax may be.

Another disturbing aspect of xMax is its apparent relation to single cycle modulation, as stated on the XG Technology web page. Single cycle modulation is a close relative of VMSK which we have discussed in an earlier post. Examination of the related patents by Bobier shows the same fatal flaw in understanding exhibited by the proponents of the VMSK idea. See the writeup by Phil Karn for example.


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